High-resolution remote sensing images are widely used in areas such as reconnaissance, geographical information system (GIS), digital city and road construction. The imaging devices that are carried on aircrafts and spacecrafts domestically and internationally, which use Time Delay Integration Charge Coupled Device (hereafter abbreviated as TDI-CCD) as the imaging target surface are called TDI-CCD cameras. TDI-CCD camera utilizes a technique that integrates the radiation energy of the same instant field of view (IFOV) on the ground m times, which is equivalent to increasing the exposure time of the same instant field of view from T to mT, but without the need to reduce the flying speed of the flying vehicles. Using this characteristic of the TDI-CCD cameras, images with geometrical resolutions higher than images obtained through single-integration technique may be obtained. The structure of the TDI-CCD cameras is a rectangular CCD array-oriented with a very large length to width ratio, which is functionally speaking equivalent to a linear array CCD. The important prerequisite for a TDI-CCD camera to obtain high-quality images is: all of the m CCD pixels having the logic relationship of delayed integration correspond to the same instant field of view, but the vibrations of the remote sensing platforms such as satellites and aircrafts prevent the imaging environment of the TDI-CCD cameras from satisfying this prerequisite. Satellites in operation have low-frequency vibrations caused by rigid body movement and middle- to high-frequency vibrations caused by the operations of the components for attitude control of the carrying capsulepayloads, for example, the vibrations caused by movements of the sun panels and the vibrations caused by the dynamic unbalance of flywheels or moment-control gyros. The vibration becomes divergent when the frequency and amplitude reach a certain critical value, thus flutter occurs. Oscillation is a very complicated physical phenomenon. For satellite platform, the oscillations of the satellite caused by perturbation could be the oscillations of a certain component, the coupling oscillations of several components, as well as the oscillations of the whole satellite. The TDI-CCD camera carried on a satellite is affected by oscillations, showing as the oscillations of the six exterior orientation elements (spatial locations (X, Y, Z) and the roll angles, pitch angles and yaw angles around the three axes x, y and z) of the camera. The irregular reciprocating translations of the camera in the three-dimensional spatial locations, the reciprocating angular vibrations around the three optical axes of the camera, and the composite motions caused by the disalignment of the optical center of the camera and the center of vibration of the flying vehicle form a very complicated process. But the results are similar: the oscillations described above cause the m CCD pixels having a logic relationship of delayed integration not to completely correspond to the same field of view, energies from different instant fields of view are superimposed as the energy from the same instant field of view, the motion blurs of imaging during flight of the flying vehicle is also superimposed, causing declines of the spatial resolutions of the remote sensing images, loss of the detail information and distortions of the pixel radiation energies. In the same oscillation environment, the higher the geometrical resolution of imaging, the larger the effect caused by oscillations on image blur. This result is contradictory to the original intention of using TDI-CCD cameras to obtain images with high spatial resolution.
In the remote sensing imaging process of the TDI-CCD cameras, M-level-integral correspond to the energy of m ground instant fields of view. If, ignoring the effect of the change of the instant field of view on the blur of the images in one integration period, using the instant field of view under an oscillation-free ideal environment as the true location, then the m instant fields of view of the ground actually obtained have misalignment errors of varying degrees relating to the true location. We further decompose this kind of misalignment errors into the following three vectors: the front (back) misalignment along the direction of integration of the TDI-CCD (the heading of the flying vehicle); the misalignment to the left and right perpendicular to the direction of integration of the TDI-CCD; the rotational misalignment rotating around the vertical axis.
Currently, the processing methods directed at image blurs are roughly direct algorithm and blind restoration algorithm, iterations algorithm. The direct calculation method is to extract motion functions from the images themselves, but because of the randomness of the excitation time of the multiple types of vibration sources, this method results in complexity and irregularity of the combined effect of the vibrations. This causes the algorithm of inversion not able to be accurate, and the result of blur removal is not satisfactory. However, although the blind restoration algorithm does not require the point spread function to be known beforehand, this algorithm needs conducting of an initial estimation of the point spread function, and the accuracy of the estimation is uncertain, and relatively good blur removal result cannot be obtained.